Miami Heat's LeBron James (L), Chris Andersen, and Norris Cole (R) stand during a break in play against the San Antonio Spurs in the third quarter during Game 3 of their NBA Finals basketball playoff in San Antonio, Texas June 11, 2013. REUTERS/Lucy Nicholson "

LeBron James has made a promise to not have a repeat Game 3 performance as his Miami Heat prepare to take on the San Antonio Spurs for Game 4 of the NBA Finals Thursday night at 9 p.m. ET.

Coming off one of the worst postseason performances of his career in Tuesday's 36-point loss to San Antonio in Game 3, James vowed to be far more aggressive amid suggestions the Spurs have knocked him off his game.

James missed 14-of-21 shots and didn't attempt a free throw for only the second time in his playoff career as the Heat suffered their worst postseason loss in franchise history, a 113-77 mauling to fall into a 2-1 series hole.

"As dark as it was last night, it can't get no darker than that, especially for me," James said Wednesday before the Heat's practice at the AT&T Center. "So I guarantee I'll be better for tomorrow (Game 4) for sure. I have to do whatever it takes. I mean, 7 for 21 isn't going to cut it. It's impossible for me to go 7 for 21, shoot 33 percent from the field and not have free throws. You have to figure out ways offensively that you can make an impact."

James acknowledged the Spurs' defensive scheme is far more complicated than it looks, and has contributed to his relative struggles throughout the series. But he also said he needs to be more aggressive and attack instead of reading the defense and waiting for openings. The 50 total points James has scored through three games against the Spurs represents his lowest point total over three straight playoff games since Miami lost to Dallas in the 2011 Finals.